Input/output (I/O) signals, power, and ground typically are routed to and from an integrated circuit (IC) package through interfaces on the bottom or sides of the IC package. For socketed packages, electrical interfaces on the bottom of the package typically mate with complementary connectors at the top surface of a socket or printed circuit board.
For example, a land grid array (LGA) package includes “land” electrical interfaces, which are substantially flat and co-planar with the bottom surface of the package. To connect the package to a socket, the package's lands are aligned with corresponding electrical mating interfaces of conductive socket contacts. Then, a sustained vertical, compressive force is applied to hold the assembly together and to ensure electrical functionality of all of the contacts. For example, a clamping mechanism might be installed to compress the package toward the socket.
For power delivery, as opposed to I/O, relatively high compressive forces are desirable to achieve lower interface resistance between the package land and the socket contacts. For a high land count LGA package and socket, this results in a compressive load requirement that has a significant impact on system design. For example, an 800 land LGA package with a typical force of 30 grams per land would require a minimum of 24 kilograms (i.e., about 53 pounds) of sustained, vertical compressive force to be applied between the LGA package and socket.
Alternatively, a pin grid array (PGA) package includes conductive pins, which extend vertically from the bottom surface of the package. The package is placed into a socket by inserting all of the pins into corresponding pin holes in the top surface of the socket. Using conventional PGA socket technologies, a horizontal “actuation force” is applied between the package and the socket to electrically engage the package pins with corresponding socket contacts. The electrical engagement of a PGA pin to its complementary socket contact requires that a sustained “normal force” be present, and this typically is a horizontal force for PGA socket technologies. This sustained normal force usually is sufficient to hold the package in place after actuation. Accordingly, no sustained vertical force typically is necessary. One disadvantage to PGA packages is that excessive force potentially may be applied on pins during handling or socket actuation, which can damage pins and result in lower yields.
Using a low insertion force (LIF) package and socket connection, conductive features on the package, which extend vertically from the bottom surface of the package, mate with complementary contacts within a socket. A vertical insertion force is used to engage a LIF package into the socket. Then the electrical engagement of a LIF package feature and socket contact requires a sustained normal force to be present, and this sustained normal force is generated when the vertical insertion force is applied. The sustained normal force generally is sufficient to hold the package in place after insertion, and a sustained, vertical compressive load between the package and socket typically is not applied.
For PGA and LIF technologies, the respective actuation and insertion force required for electrical engagement can be quite large. For example, an 800 contact LIF package could require a typical value of 60 grams of vertical insertion force per contact, thus requiring a minimum of 48 kilograms (i.e., approximately 106 pounds) of vertical insertion force between the LIF package and socket.
What are needed are packaging interconnection technologies, which require lower insertion and/or actuation forces while ensuring sufficient contact normal forces throughout a device's operational range. Further needed are packaging interconnection technologies, which benefit from the advantages provided by compression-type contacts (e.g., LGA) and insertable-type contacts (e.g., PGA and LIF), without the high actuation or insertion force disadvantages inherent in using these connection types.